human hunted sea cows => the author's point of view
extirpation of sea otter海獭灭绝 => explosion of sea urchin海胆增多 => eat all the kelps 褐藻灭绝=> no kelp for sea cow to eat海牛饿死 {the alternative explanation that the auhtor disagreed}
文章很短，大家看intro就好，后面data神马的不用管..
